diff --git a/pvmfitOptions.h b/pvmfitOptions.h
index 59d6c8359625882052b58977e325f9ed1f5cb923..a323325e7ea2a3de897f7e7b68aa094fe83373e3 100644
--- a/pvmfitOptions.h
+++ b/pvmfitOptions.h
@@ -79,7 +79,7 @@ class pvmfitOptions {
 	     true, requires_argument), 
    nfibres(string("-n,--nfibres"), 1,
 	     string("number of fibres to fit - default=1"),
-	     true, requires_argument), 
+	     false, requires_argument), 
    options("pvmfit", "pvmfit -k <filename>\n pvmfit --verbose\n")
    {